Dysfunctional stem cells are a telltale sign of aging, particularly in a dynamic organ such as the gut. The gut epithelium indeed requires constant regeneration throughout an animal?s lifespan to maintain its functionality in the face of the wear and tear of digestion. The gut and its stem cells need to recognize and adapt to variations in the luminal content, which comprises food, microbes and xenobiotics. However, the key signals, receptors and pathways underlying environmental sensing by intestinal stem cells (ISCs) remain largely unknown. We propose to use the powerful genetic model organism Drosophila melanogaster (Dmel) to investigate this question in vivo. Our preliminary data show that chemosensory proteins, specifically gustatory and olfactory receptors (GRs and ORs, respectively), are expressed in Dmel midgut progenitor cells. In addition, we found that progenitor-specific lack of one of these receptors, Gr28a, results in age dependent impairment of ISC-mediated epithelium renewal and an overall decreased lifespan. These results therefore suggest that progenitor cells can ?sense? and respond to their environment directly, through the use of smell and taste receptors. In this proposed research, we aim to characterize the role of GRs and ORs that are expressed in progenitor cells and determine how they affect ISC activity and organismal lifespan. We also aim to identify the ligands of these receptors as they could allow nutritional intervention to modulate ISC activity and expand lifespan. Altogether, we will test the hypothesis that these receptors provide a means for progenitors to sense chemical cues in the lumen and adjust ISC proliferation and differentiation accordingly, thus maintaining gut integrity and increasing lifespan. We propose four aims to explore how progenitor cells sense their environment through GR/ORs, in order to maintain optimal intestinal function and longevity. We will first characterize the impact of Gr28a on ISCs and lifespan through genetic manipulation (Aim1). We will then evaluate the molecular cues that modulate ISC activity through Gr28a by using chemically defined diets and by manipulation of the microbiota (Aim2). Next, we will characterize the downstream genetic components that mediate the Gr28a phenotype by coupling transcriptomic analyses and testing epistatic interaction between Gr28a and candidate genes identified in our transcriptome analysis (Aim3). Finally, we will explore the impact of a panel of additional GR/ORs in regulating ISCs (Aim4). Altogether, we will identify new nutritional and microbial molecular cues that control ISCs, as well as the cellular receptors that mediate these effects. These experiments will demonstrate a role for GRs/ORs in the control of ISCs and provide new mechanistic insight into the complexity of the interactions between ISCs, nutrients and gut microbes. This work will therefore improve our understanding of how diet and microbes can impact epithelial homeostasis in health, disease and aging. These concepts can be readily transferred to mammalian systems and serve as a paradigm for the development of therapeutic strategies aimed at optimizing ISC activity and expanding lifespan.